Wearable near-to-eye display system for workers have long seemed to be on the verge of commercial success, but to date, acceptance has been limited. The main reason is that the images presented to the human brain through the eyes are not as natural as the images sensed by the eye causing eye strain and/or nausea. Several factors contribute to this unnatural sensation.
First factor is tunnel vision. Human eyes cover a wide field of view, a total binocular field of view (FOV) of about 120 degrees horizontal (180 degrees forward facing horizontal) by 130 degrees vertical. Normal camera covers up to 60 degrees FOV. Optical design to replicate human visual FOV is possible but creates a very bulky and heavy system which is not suitable for a wearable display. Therefore existing commercial off the shelf (COTS) wearable, one-camera, near-the-eye display systems offer a narrower FOV and the user suffers with tunnel vision.
Another factor causing unnatural sensation includes incorrect focus of the scene. Human eyes are capable of instantaneously switching focus on objects in the scene from far field to near field. Autofocus camera exists which provide a solution. Such cameras, however, have complex lens systems and drivers. Again the requirements on size, weight and power make the autofocus feature not-suitable for a wearable display. Fixed focus cameras yield blurry images when the subject of interest is beyond the depth of field of the current focus distance.
Another factor that influences the acceptance of a wearable display system is incorrect viewing perspective. The inter-pupillary distance (IPD) of adults ranges from 5.5 to 7.0 cm. If the cameras are placed at locations other than the center of the pupils, the acquired images will have a different perspective than that of the eyes. This different perspective creates an impression/sensation that the eyes are stretching or squinting all the time.